Electric train control equipment



Dec. 15, 1931. LUDDECKE 1,836,330

ELECTRIC TRAIN CONTROL EQUIPMENT Filed July 8, 19:50 2 Sheets-Sheet 1 Fig.1

2 Sheetsheet 2 Fig. 5

Dec. 15, 1931.

Fig.6

Patented Dec. 15, 1931 UNITED sr rEs PATENT OFFICE KARL nt'mnnoxn, on BERLIN-SIEMENSSTADT,GERMANY, ssIGNon TO V REINIGTE EISENBAIELN-SIGNALWERKE, G-ESELLSCHAF'I" MIT BnsoHnANKTEaa HAFTUNG, or, sIEMENssrAnr NEAR BERLIN; GERMANY, A CORPORATION on GERMANY nnno'rarc TRAIN ooN'raor. EQUIPMENT Applicationfiled July 8, 1930, Serial No. 466,456, and in Germany August 13, 1929.

My invention relates to electric train con trol equipment, more particularly for tracks with low insulation resistancebetween the rails and the ground.

There are already known train control equipments in which control currents flowing in the rails act continuously upon the travelling train (track circuit train control) Such equipment may be used in conjunction with the automatic block section system, a control circuit being employed apart from the block circuit for operating the track signals;

The application of the block current which traverses both rails of a track in opposite direction presumes that the rails are laid on wooden ties and rest upon a ballast which possesses a sufficiently high insulation resistance, in order to keep the ballast currents as low as possible and to enable the rail current to flow with as small a loss as possible to the end of thetrack section and intothe block relay. In the case of tracks or railroads laid on steel ties and ballast of low insulation resistance the block current and the control system suitable for the automatic block section with two rail currents isnot directly. applicable.

To permit a line control on tracks with such unfavorable insulation conditions in which the block current is not applicable, more particularly on tracks with steel ties, one is confined to the control current alone which flows in both rails in the same direction and withsubstantially equal intensity, and is thus not afiected by the axles of a train. This control current may by suitable connection be made dependent uponthe position of the hand-operated signals and be utilized for transmission to the travelling train.

Previous attempts to make a current flow through both rails in the same direction across a definite length of the track encountered difficulties by reason of the low insulation resistance between the railsand the ground. This may be accounted for by the fact that due to so-called skin or Kelvin effect solid conductors oifer a considerably higher resistance to alternating current than to direct current, and that on the other hand the contact resistance from the rails and steel ties across the ballast to the ground is comparatively low.

At the beginning of such a track section the alternating current. supplied to the rails thus easily leaks to ground and only at the end of'the section returns into the rails and across the feeder to the source of current. In the middle of this track section thus remains only a small portioniof the current, while the ground leakage currents which hardly find. any resistance in the ground, form the main the contact resistances dependent upon the weather. The potential of the rails to ground is therefore positive at the point where the current flows into the track section, negative 5 portion of the current applied according to at the end of the section where the current A flows out of the section and zero approximately in the middle (assuming homogeneous distribution of the contact resistances of the track to ground) so that at the beginning and the end of the fed section there exists a potential to earth of about half the total potential drop of the section. The value Of'the rail and ground currents depends, however, upon this difference in potential. With the increase of the length of the track grows, however, the resistance of the rails, while the contact resistance from the rails to ground diminishes due to the broadening of the contact area. The ratio of the stray ground currents to the remaining rail currentthus grows with the square of the length of the track. For this reason it was, in a comparatively long track tire block section but stepwise short distances apart. In this way the potential difference between the rails and the ground may be so limited that it does not exceed a definite amount on the positive and negative side.

wherebylhegmundcurrenlsnybereduced to a minimum. (Since alternating current is concerned the term positive and negative holds good for a definite instantaneous value only.) In order to avoid controlling the rail currents for the entire block section in each subsection individually, the connections may, according to a further feature of my invention, be so arranged, that the transformers for feeding the individual sections are controlled on the primary side by a common switch or contact from the control station (locking frame, signal, relay, or the like).

Several examples for these connections and curves which show the course of the potential and the rail currents along the block section are illustrated in the drawings ai'iixed to my specification and forming part thereof.

In these drawings:

Fig. lrepres'ents a diagram showing the subsectional divisions of the track and the circuit connections for the current supply;

Figs. 2 and 3 represent graphs showing respectively-the potentials and the current intensities prevailing along the sub-sections of the track;

Fig. 4 represents a modified circuit arrangement for the current supply to the sub-sections Fig. 5 represents a modified circuit arrangement in which the rails of track subsections are not insulated from one another;

Fig. 6 represents a simplified form of the arrangement shown in Fig. 5, and

Fig. 7'represents a graph showing the potentials existing along the several track subsections inthearrangements of Figs. 5 and 6.

Fig. 1 ofthe drawings shows av block section B with adjacent block sections A and C. The

i entire main section B is divided for instance into three sub-sections, each of which is insulated from the other as shown at 2, and each of which is supplied with control current by a section transformer 6 through individual circuits, including in each case a secondary winding 8, a lead 4:, a'rail cross-connector 3, both rails 1, cross-connector 23, a return line 5,winding 8. These circuits are not equipped with switches or contacts. The individual section transformers 6 are fed from a feed transformer 11 common to themall by the feeder 9 in such a way, that their primary windings 7, which are connected in this modification in parallel, can be disconnected by the a switch 10, which may be operated in suitable manner (not shown) from the locking frame or, for instance, through the corresponding section signal, whereby all subsections and thus the entire main section B becomes dead.

By the aforementioned insulations 2 be tween the sub-sections the voltage and the rail currents of each individual subsection become independent of those in the adjacent section. From this results the stepwise course of the potential of the rails to ground shown I I l I V y I i lnllgloltluuh'awmgs. 1.110551%01the number of the subsections of a block section the smaller the potential drop 6 along the rails and the smaller the current leakage from the rails into the ground.

Fig. 3 of the drawings shows a. diagram of the track currents along the block section B in which T indicates the current supplied to the rail, T the current remaining in the rails, and T the ground current. Since at the beginning of a track section a portion of the total current T flows from the rails into the ground and, conversely, at the end of the section returns from the ground into the rails, the rail current is smallest at about the middle of the section and the ground current largest. From the practically permissible ratio between the ground and rail currents follows the necessary number of divisions of the block section into individual subsections.

Another system of connections which gives the same result is illustrated in Fig. t of the drawings. Here negative boosting or suction transformers are employed which are well known in the art for other purposes. These suction transformers are in principle similar to the current transformers but their transformation ratio is approximately 1:1. They are so connected that the control current flowing from the feed transformer 11 across the switch 10 is at the beginning of the block section B supplied. over a lead 4* and cross-connector 3 to the rails 1 of the first subsection from where it returns across the line 5 through the secondary winding 8 of the first suction transformer 6, whence it flows through lead 4 through the rails of the second sub-section to the secondary 8 of the next transformer, and so on to the end of the block section, at which point it leaves the section through lead 5 and flows through the primary windings 7 of all suction transformers (3 in series by way of return line 9. The sub sections 1 are again insulated from one another by insulating joints 2.

In contrast with the embodiment illustrated in Fig. 1, there exists in Fig. 4; a single circuit only which comprises the entire block section. The same current thus traverses the primary and the secondary windings of all suction transformers. By suitably proportioning'their windings a voltage 0 will then be produced in the secondary winding 8 of each transformer which compensates the potential drop of a track sub-section and thus effcct-s a stepwise potential drop in the rails according to Fig. 2. The action of the suction transformers may be so conceived that the currents, otherwise flowing in the ground, are by this increase in the voltage, as it were, sucked up and forced into the rails, so that a current characteristic is produced as shown by the graph in Fig. 3 of the drawings. For compensating a phase displacement between the currents flowing in the primaries and secondaries, caused by the magnetization of the suction transformers, ohmic resistances 12 of suitable value may be connected in parallel with the primary windings 7. A substantial advantage of this mode of connection resides in the fact that only a single line 9 is required along the entire block section.

The two embodiments described so far and illustrated in Figs. 1 and 4 of the drawings require that the individual sections be insulated from one another by insulated joints. This insulation may be avoided if care is taken that this stepwise voltage increase does not take place abruptly but gradually.

Such an embodiment of my invention is illustrated in Fig. 5 of the drawings. The system of connections is in principle identical with that illustrated in. Fig. 1. It differs from it only in so far as the secondary windings 8 of the section transformers 6 are according to my invention successively reversed in polarity.

As Fig. 7 shows, this has the result that the potential difference drops in the first section, rises in the second, and drops again in the third section and so on. The direction of the current in the rails thus changes from one section to the other, which in the ordinary transmission to the receiving apparatus on the train is immaterial. Since in this arrangement the end of one section and the beginning of the adjacent section have the same potential to ground, both connections to the rail sections may be made by a common line, instead of two separate lines such as 4 and 5 in Fig. 1. This possible alternative arrangement has, however, not. been illustrated. The differential connection of the secondaries of the section transformers 6 which is indicated by the direction of the arrows is made by successively changing the polarity of the primary windings 7 at their connections to the feeders 9. The electrical disconnection of the individual track sections again takes place by a common switch 10 in the feeding line 9 by which the entire block may be made dead. Since on disconnecting the section B, for instance, there exists only a small potential dif ference to ground at the end of the section A and at the beginning of the section C, the potential of which is now assumed by the dead section B and since in consequence thereof an increase in the ground currents and thus a reduction of the rail currents would occur in the adjacent track sections A and C, it is advisable to insulate each block section against the adjacent section, in order not to affect the course of the current adversely. These insulating joints are shown at 2 in Fig. 5.

A simplification of the last described system of connection is illustrated in Fig. 6, in which according to my invention always two subsections are fed by a single section transformer; Thedifferential connection of the individual transformers is here avoided and all transformers of one block, the number of which is reduced to one half, are connected with like polarity to the feeder of the feeding transformer 11. The feeder 13 may at the.

same time serve as return linefor the rail currents byconnecting one end of the primary 7 and the secondary 8 of each section transformer 6 to this common line. The other terminal of the secondary 8 of each transformer 6 is connected between the members of each sub-section pair by the rail cross connection 23, and the feeder 13 is connected by the cross connector 3 to the junction point between two adjacent sub-section pairs. The currents will then flow throughv the individual sub-sections as indicated by 'the arrows.

The course of the voltage along the track corresponds then with that of the system of connections according to Fig. 5 and occurs as illustrated in Fig. 7.

Iclaim as my invention:

1. 111 an automatic train control system having a track section divided into a plurality of sub-sections, a source of control current, means for feeding said current to each of said sub-sections to flow in the same direction in both track rails of each sub-section for controlling a train traversing the section, and means for compensating the potential drop in each sub-section due to ground leakage currents tending to flow between the ends of the sub-sections.

2. In an automatic train control system, having a track section divided into a plurality of sub-sections conductively connected with .one another, a source of control current and transformers for supplying said current to said sub-sections for controlling a train traversing said track section, said transformers being connected to. said sub-sections and to said source, so that the current flows in the two track rails of each sub-section in the same direction but traverses adjacent subsections in opposite directions, for compensating the potential drop in each sub-section due to ground leakage currents tending to flow between the ends of the sub-sections.

3. In an automatic train control system, having a track section divided into a plurality of sub-sections conductively connected with one another, a source of control current and transformers for supplying said current to said sub-sections for controlling a train traversing said track section, one transformer being provided for each pair of adj acent sub-sections and being connected at the junction of the pair members, and being connected to said source, so that the current flows in opposite directions through the members of each pair, but in the same direction in both rails of each member, whereby the potential drop in each sub-section, due to ground leakage currents tending to flow between the ends of the sub-sections, is compensated.

4. In an automatic train control system, having a track section divided into a plurality of sub-sections conductively connected with one another, a source of control current and transformers for supplying said current to said sub-sections for controlling a train traversing said track section, one transformer being provided for each pair of adjacent sub-sections, the secondary of each transformer being connected With one terminal to the junction point of the pair members, the other terminal of the secondary and one terminal of the primary of all transformers being connected by a common lead to said source, and a connection between the junction points of adjacent sub-section pairs and said common lead, so that the current flows in opposite directions through the members of each pair, but in the same direction in both rails of each member, whereby the potential drop in each sub-section, due to ground leakage currents tending to flow between the ends of the sub-sections, is compensated.

5. In an automatic train control system, having a track section divided into a plurality of subsections conductively connected with one another, a source of control current and transformers for supplying said current to said sub-sections for controlling a train traversing said track section, the secondaries of said transformers being connected to the ends of their pertaining track sub-section, the primaries of said transformers being connected to said source in parallel relation to one another, the primaries of successive sub-sections being connected to said source with reversed polarity, so that the current flows in the two track rails of each sub-section in the same direction but traverses adjacent sub-sections in opposite directions, for compensating the potential drop in each subsection due to ground leakage currents tending to flow between the ends of the subsections.

KARL LUDDECKE. 

